Late radiation toxicity in Hodgkin lymphoma patients: proton therapy's potential

Abstract

In 2010, all young patients treated for intrathoracic Hodgkin lymphoma (HL) at one of 10 radiotherapy centers in the province of Quebec received 3D conformal photon therapy. These patients may now be at risk for late effects of their treatment, notably secondary malignancies and cardiac toxicity. We hypothesized that more complex radiotherapy, including intensity-modulated proton therapy (IMPT) and possibly IMRT (in the form of helical tomotherapy (HT)), could benefit these patients. With institutional review board approval at 10 institutions, all treatment plans for patients under the age of 30 treated for HL during a six-month consecutive period of 2010 were retrieved. Twenty-six patients were identified, and after excluding patients with extrathoracic radiation or treatment of recurrence, 20 patients were replanned for HT and IMPT. Neutron dose for IMPT plans was estimated from published measurements. The relative seriality model was used to predict excess risk of cardiac mortality. A modified linear quadratic model was used to predict the excess absolute risk for induction of lung cancer and, in female patients, breast cancer. Model parameters were derived from published data. Predicted risk for cardiac mortality was similar among the three treatment techniques (absolute excess risk of cardiac mortality was not reduced for HT or IMPT (p > 0.05, p > 0.05) as compared to 3D CRT). Predicted risks were increased for HT and reduced for IMPT for secondary lung cancer (p < 0.001, p < 0.001) and breast cancers (p< 0.001, p< 0.001) as compared to 3D CRT.

Figure 1

Patient case (Patient 7) demonstrating nonsignificant reduction in predicted risk of cardiac mortality for HT (middle) and IMPT (right) as compared with 3D CRT (left). PTV contour in red, heart contour in yellow. Relative DVH for heart for each modality shown on right.

Figure 2

Patient case (Patient 18) demonstrating pronounced reduction of risk for cardiac mortality for HT and IMPT as compared with 3D CRT (left). PTV contour in red, heart contour in yellow. Relative DVH for heart for each modality shown on right.

Figure 3

Patient case (Patient 7) exhibiting reduction in risk for lung cancer for IMPT and increase in risk for lung cancer for HT as compared to 3D CRT. PTV contour in red. Relative DVH for lungs for each modality shown on right.

Figure 4

Female patient case (Patient 7) exhibiting reduction in risk for breast cancer for IMPT and increase in risk for breast cancer for HT as compared to 3D CRT. PTV in red. Relative DVH for breasts for each modality shown on right.

Figure 5

Risk for cardiac mortality, lung cancer, and breast cancer for HT (black circles) and IMPT (red crosses) relative to 3D CRT for all patients in the study.